1. Field of the Invention
The present invention relates to a sulfur cross-linkable unvulcanized rubber mixture for the production of treads, in particular for snow tires, which contains the rubber mixture components polyisoprene, polybutadiene and styrene-butadiene copolymer as well as further fillers and additives.
2. Discussion of Background Information
Since the driving characteristics of a tire depend to a great degree on the rubber composition of the tread, particularly high demands are placed thereon. Optimizing these characteristics is difficult, in particular for snow tires which, on the one hand, must exhibit good traction capabilities on snow and ice as well as on wet road surfaces, but on the other hand should show little roll resistance and little abrasion. It has been determined that the fillers which are used have a critical effect on the driving-behavior characteristics of the winter tire.
Rubber mixtures for treads containing only carbon black exhibit a balanced relationship between their behavior on wet and wintery road surfaces, but not, however, at a satisfactory level. In addition, winter tires are known in prior art whose treads consist of rubber mixtures which contain silicic acid as part of the fillers material. With these mixtures, winter tires with improved wet characteristics are created--an improvement in the winter characteristics is, however, not possible, so that such mixture systems are also not optimally suited.
In DE 44 42 691 and DE 44 42 692, rubber mixtures for treads are disclosed whose rubber components are emulsion- or solution- polymerized styrene-butadiene copolymer, polyisoprene, and polybutadiene. Silicic acid (25-90 weight parts) or carbon black should be used as the filler. It has been shown, however, that these rubber mixtures are not sufficiently suited for winter tires, since the use of emulsion-polymerized styrene-butadiene copolymer causes a worsening of the winter characteristics and further causes greater abrasion.